Incremental test code changed by a diff

[sourcefrog]

Given a diff (e.g. of uncommitted or unmerged changes) test only mutants that intersect with changed regions.

[linear]

MUT-39 Incremental test changes in a diff

Elsewhere:

https://mull.readthedocs.io/en/0.21.0/IncrementalMutationTesting.html

Later: automatically run git diff to get the diff?

• Find (or write?) some Rust library to parse the diff into lines
  • Maybe https://docs.rs/patch/latest/patch/struct.Patch.html#method.from_multiple
• Take a diff as an option
• Explore/document how to use this with diff?
• Filter mutants that intersect with any of the "after" line numbers?
• Check the "after" of the diff matches the current source; maybe warn if it does not because the diff might be out of sync with the source?

Maybe/later:

• Automatically run git to get the diff?

I thought about reading only affected files, but in general we have to parse many of them to find sub-modules. I guess we could read affected modules or those that are plausibly parents of them… In general it seems very cheap.

[sourcefrog]

merged in 9e2833d